Nutritional and developmental studies in pecan: studies on zinc, nitrogen, and seasonal fluctuation of carbohydrate and nutrients
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Studies were conducted in pecan (Carya illinoinensis Wangenh. K. Koch) including 1) the effect of zinc supply on growth, development, and nutrient uptake of different seedstocks, 2) evaluation of zinc deficiency at macro- and microscopic levels, 3) the effect of different nitrogen sources on growth, development and nutrient uptake, and 4) seasonal changes in nutrients and carbohydrates. Zinc efficiency was compared in two pecan seedstocks, _Stuart _ and _Curtis _. _Stuart _ exhibited more severe deficiency ratings than _Curtis _. _Stuart _ seedstocks grown under minus zinc versus plus zinc conditions exhibited significantly higher foliar concentration of P, Ca, Mg, and Cu, while _Curtis _ leaves contained significantly higher Mn and lower S. A microscopic evaluations of zinc deficiency were conducted using light and transmission electron microscopy. Zinc deficiency symptoms varied with severity ranging from interveinal mottling, overall chlorosis, necrosis, to marginal curving. Changes in leaf thickness and mesophyll cell organization were associated with zinc deficiency. Cells in zinc deficient leaves had limited cytoplasmic content and accumulated phenolic compounds in vacuoles. Extensive starch accumulation was observed in chloroplasts. This work represents the first detailed microscopic evaluations of zinc deficiency in leaves. The effects of nitrogen form on plant growth and nutrient uptake were evaluated. Plants grown with a 75:25 (ammonium:nitrate) ratio exhibited significantly lower biomass, decreased root/shoot ratio, and lower specific leaf weight than observed in lower ammonium treatments. The highest root growth was observed in the 50:50 ratio treatment. Levels of Ca, Mg, and Mn in leaves were higher in 25:75 than in 75:25. Total nitrogen uptake on a dry weight basis was highest in the 75:25 treatment. Plants exhibited preferential uptake of ammonium nitrogen under all nitrogen regimes. Changes in soluble carbohydrate levels were related to leaf and fruit developmental stages. Glucose level declined during cotyledon elongation and reserve deposition in fruit. Fructose levels declined during fruit storage reserve accumulation. After fruit maturation, stems exhibited a dramatic increase of sucrose along with a marked decrease of starch. Seasonal variation of essential element levels in leaves indicated developmental stage-related nutrient movement. During leaf development, all essential elements accumulated in leaves.